Evolved radio access schemes and radio networks for cellular mobile communication (hereinafter referred to as “Long Term Evolution (LTE)” or “Evolved Universal Terrestrial Radio Access (EUTRA)”) are being studied by the 3rd Generation Partnership Project (3GPP). In LTE, the orthogonal frequency division multiplexing (OFDM) scheme is used as a communication scheme for the downlink from a base station device to a mobile station device. Furthermore, the SC-FDMA (Single-Carrier Frequency Division Multiple Access) scheme is used as a communication scheme for the uplink from a mobile station device to a base station device. Here, in LTE, a base station device is also called eNodeB (evolved NodeB), and a mobile station device is also called UE (User Equipment). LTE is a cellular communication system in which a plurality of areas, each of which is covered by a base station device, are arranged in a cellular configuration.
In LTE, a mobile station device calculates channel state information on the basis of a downlink reference signal received from a base station device. The mobile station device transmits the channel state information to the base station device using a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH).
In LTE, a base station device schedules a physical downlink shared channel (PDSCH) in accordance with channel state information received from a mobile station device. Further, the base station device transmits information indicating the result of scheduling to the mobile station device using a physical downlink control channel (PUCCH). The mobile station device performs a reception process for the PDSCH in accordance with the received information indicating the result of scheduling.
In LTE, a technology for providing communication between a mobile station device and a base station device using a plurality of cells (component carriers) having the same channel structure (also referred to as cell aggregation or carrier aggregation) is used. For example, in communication using cell aggregation, a mobile station device and a base station device can simultaneously transmit and receive a plurality of physical channels using a plurality of cells. For example, after the initial connection is established between a mobile station device and a base station device within one cell, the base station device can add a cell to be used for communication with the mobile station device.
In LTE, a base station device can configure, for a mobile station device, periodic channel state information reports for a plurality of cells. The base station device transmits information indicating the configured periodic channel state information reports for the plurality of cells to the mobile station device. The mobile station device configures the periodic channel state information reports for the plurality of cells on the basis of the information indicating the configured periodic channel state information reports for the plurality of cells. The mobile station device for which the periodic channel state information reports for the plurality of cells have been configured periodically transmits channel state information corresponding to each of the plurality of cells using the PUCCH. If periodic transmissions of a plurality of pieces of channel state information have collided in a given subframe, the mobile station device transmits one of the plurality of pieces of channel state information to the base station device, and drops (does not transmit) the other pieces of channel state information. Thus, the base station device is not able to schedule the PDSCH on the basis of channel state information for the cells corresponding to the channel state information that the mobile station device has dropped. Accordingly, a problem occurs in that efficient scheduling of the PDSCH is not achievable.
In 3GPP, the transmission of a plurality of pieces of channel state information using new PUCCH formats or a PUSCH is being studied.